This invention relates to electrostatographic reproduction machines, and more particularly to a process cartridge for use in an electrostatographic reproduction machine. Specifically this invention relates to such a cartridge including a charge metering blade. In an embodiment, the blade includes an elastomeric surface tailored to enhance toner's charge prior to transfer to an imaging member. In a particularly preferred embodiment, the charge metering blade has a polyurethane base and a low surface energy coating thereon.
Generally, the process of electrostatographic reproduction includes charging an imaging member to a substantially uniform potential so as to sensitize the surface thereof. A charged portion of the photoconductive surface is exposed at an exposure station to a light image of an original document to be reproduced, thereby producing a latent image of the original image onto the imaging member. The recorded latent image is subsequently developed using a development apparatus by bringing a charged dry or liquid developer material into contact with the latent image. Two component and single component developer materials are commonly used. A typical two-component dry developer material has magnetic carrier granules with fusible toner particles adhering triobelectrically thereto. A single component dry developer material typically comprising toner particles only can also be used. The toner image formed by such development is subsequently transferred at a transfer station onto a copy sheet fed to such transfer station, and on which the toner particles image is then heated and permanently fused so as to form a "hardcopy" of the original image.
It is well known that a number of the elements and components of an electrostatographic reproduction machine can be combined to form a customer or user replaceable unit CRU. Typically such units are each formed as a cartridge that can be inserted or removed from the machine frame by a customer or user. Reproduction machines such as copiers and printers ordinarily include consumable materials such as toner, volume limiting components such as a waste toner container, and life cycle limiting components such as a photoreceptor and a cleaning device. Because these elements of the copying machine or printer must be replaced frequently, they are more likely to be incorporated into a replaceable cartridge.
In single component development as described above, the particle of toner is charged prior to development of the toner onto the photoreceptive drum by rubbing the particle between a charge-metering blade and a donor roll. The charged particles on the periphery of the donor roll are then transferred onto the imaging member at the charged portions of the surface of the imaging member or the latent image to form the developed image on the imaging member. The developed image is then transferred onto a copy substrate, such as paper.
In the process of transferring the toner from the surface of the donor roll onto the paper, some of the toner remains on the surface of the donor roll. The toner, which remains on the surface of the donor roll, has a residual charge that may accumulate on the donor roll. When the surface of the magnetic roll is exposed to toner from the sump to be reloaded for further image development, the toner which remains on the surface of the donor roll combines with fresh toner from the sump. These accumulated or residual charges are not uniformly distributed on the periphery of the donor roll, and in fact, correspond to the developed image of the imaging member. These accumulated or residual charges cause less toner to be attracted to the periphery of the donor roll at areas which correspond to a concentrated or solid developed image of the imaging member. The result is ghosting or underdevelopment of an area upon the substrate or paper.
Such ghosting phenomenon is more acute in solid area development where large areas are required to have a dark or solid image. The accumulated or residual charges reduce the amount of fresh toner attracted onto the magnetic roll. Therefore, some areas have a lighter than desired image.
The surface of the blade may also become contaminated with toner material that is advanced by the donor roll and passes by the surface of the blade. This contamination occurs because the toner will not separate from the surface of the blade. In fact, long clusters of toner may form on the blade. These clusters have a greater tendency of forming at the edge of the blade. As these clusters form on the blade, the clusters of toners deplete the donor roll or clean the layer of toner from the donor roll. The portion of the donor roll which has been depleted causes streaks to occur on the latent image, and therefore, the copy substrate.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 5,663,788, Patentee: Sanpe, Issue Date: Sep. 2, 1997; PA1 U.S. Pat. No. 5,605,777, Patentee: Ando, et al., Issue Date: Feb. 25, 1997; PA1 U.S. Pat. No. 5,548,382, Patentee: Koshi, et al., Issue Date: Aug. 20, 1996; PA1 U.S. Pat. No. 5,400,128, Patentee: Michlin, Issue Date: Mar. 21, 1995; PA1 U.S. Pat. No. 5,363,182; Patentee: Kuribayashi, et al., Issue Date: Nov. 8, 1994; PA1 U.S. Pat. No. 5,357,317, Patentee: Fukuchi, et al., Issue Date: Oct. 18, 1994; PA1 U.S. Pat. No. 5,220,129, Patentee: Nishio, et al., Issue Date: Jun. 5, 1993; and PA1 U.S. Pat. No. 5,097,294, Patentee: Nishio, et al., Issue Date: Mar. 17, 1992.
U.S. Pat. No. 5,663,788 discloses an electrostatic image forming apparatus having high cleaning efficiency using the electrostatic fur brush method.
U.S. Pat. No. 5,605,777 discloses a predetermined processing liquid supplied by a liquid supplying unit to a sheet of transfer paper having a surface on which toner is stably attached.
U.S. Pat. No. 5,548,382 discloses a developing device using a one-component developer.
U.S. Pat. No. 5,400,128 discloses in toner cartridge assemblies for use in copiers, printers and facsimile machines, a conductive coating which is applied to the wiper and spreader blades. The wiper blade has a coating comprising polytetrafluoroethylene (TEFLON.RTM.) made conductive by the addition of a conductive substance.
U.S. Pat. No. 5,363,182 discloses a blade device for use in contact with an object such as an image-carrying photosensitive drum of an image forming apparatus. The blade device has a blade body made of urethane rubber, a surface coating layer and an underlying primer layer.
U.S. Pat. No. 5,097,294 discloses a developing device including a blade member provided within the vessel and is resiliently engaged with the developing roller for regulating a thickness of the developer layer formed therearound.